U.S. Pat. No. 4,885,739, entitled "Interprocessor Switching Network", assigned to the present assignee, describes a digital switching network for handling data transfers among a number of processors. The system is designed to accommodate a large number of simultaneous connections at fast connection rates. Connections are via a switching matrix, and the data transmission uses packet switching techniques. The switching network is used to make connections for communicating messages within a distributed system of data stations, such as systems of computers or telephones with related supervisory and peripheral equipment. At each data station, clusters of processor-based user equipment originate and receive messages.
The switching network described in U.S. Pat. No. 4,885,739 is characterized by several hardware features, including node controllers for handling nodes of cluster processors, gateways for providing an interface for the node controllers into the switching matrix, an interchange control system, and an interchange that includes the switching matrix. It is also characterized by the use of a multi-level communications protocol, having at least three levels. A first level handles communications between a gateway and the switching system. A second level handles communications between node controllers. A third level handles communications between cluster processors.
Typically, the node controllers in switching networks such as described in U.S. Pat. No. 4,885,739 are interrupt driven. Interrupt signals trigger processes that set up a communications path and send and receive the data. Although this technique works well in practice, as the number of data stations increases, so does the complexity of the switching process. The generation and communication of the various control and data messages requires increased processing overhead.
To meet the demands of increased message volume, existing systems attempt to accomplish real time processing with a high interrupt rate. An interrupt occurs once for every processing event. Thus, during the time between the sending of a message from an originating cluster processor and the receipt of the message at a destination cluster processor, a number of interrupts may occur. Faster message processing rates are attempted by increasing the interrupt rate. However, a problem with faster interrupt rates is that fewer events can be processed during each interrupt period. Unprocessed events must be queued for processing at a later time. Dequeueing occurs during "catchup periods" when the rate of originating messages slows. Thus, waiting times and overall throughput become a function of probability and statistics.
A need exists for an improved method of using a switching network to handle a large number of messages in a given time.